The present invention relates to an ink-furnishing apparatus, which furnishes ink stored in an ink fountain to an ink furnishing roller that is brought into contact with a plate cylinder, and an offset printing method using the same ink-furnishing apparatus.
FIG. 20 shows a general construction of a prior art ink-furnishing apparatus for an offset press. Ink stored in an ink reservoir is led to an ink transfer roller 904 side by rotations of an ink furnishing roller 903. By causing the ink transfer roller 904 to alternately be brought into contact with the ink furnishing roller 903 and the top roller of a group of ink mixing rollers 905, an ink membrane formed on the surface of the ink furnishing roller 903 is transferred onto respective rollers of the group of ink mixing rollers 905 one after another, and is fed onto the surface of a plate cylinder 901 via an ink application roller 902. Further, an aqueous membrane is formed on the surface of a non-imaged portion of the plate cylinder 901 by a dampening device 506, wherein no ink is transferred onto the non-imaged portions.
Since the above-described offset press ink is intermittently fed by swinging of the ink transfer roller, it is necessary that a uniform membrane of ink is formed while gradually transferring ink by a number of rollers of the group of ink mixing rollers, and the uniform membrane of ink is fed onto the surface of the plate cylinder. Therefore, the apparatus is complicated and large-sized, resulting in maintenance difficulty and an increase in production costs.
In order to solve the above-described problem incidental to intermittent furnishing of ink, offset presses disclosed by Japanese Unexamined Patent Application Publication Nos. 58-45955, 58-65663, and 58-84771 have been publicly known. In either of these offset presses, continuous furnishing of ink is employed, thereby removing a group of ink mixing rollers, wherein the apparatus is simplified and small-sized, maintenance thereof is facilitated, and production costs thereof are decreased.
However, since no group of ink mixing rollers is provided, an ink reservoir is located in the vicinity of a dampening device, wherein ink is remarkably emulsified to worsen the printing density, that is, so-called xe2x80x9cemulsificationxe2x80x9d occurs. Also, a dampening water is likely to be mixed in the ink reservoir. In the worst case, roller stripping occurs, for which the ink is not permitted to be applied onto the ink furnishing roller better, and there occurs a possibility for ink not to be measured and fed. In order to avoid this roller stripping, accurate adjustment of the dampening water device is indispensable. However, the stabilized area thereof is very narrow, and there may be a case where the adjustment is disabled, depending upon specified combinations of ink to be used and the dampening water.
An offset press disclosed by Japanese Unexamined Patent Application Publication No. 55-7453 has been publicly known as such a type that can solve the above-described problems resulting from the dampening water. The offset press does not require the furnishing of the dampening water by employing emulsion ink (which is a colloid in which ink and an aqueous constituent are blended) as ink, wherein it is possible to prevent a roller stripping phenomenon from occurring, and no dampening water device is required. Further, it is possible to simplify and make the apparatus small, and to simplify maintenance and to decrease production costs.
In offset printing for which emulsion ink is used, it is necessary to break emulsion in order to divide the emulsion ink into ink constituents and aqueous constituents at the stage where the emulsion ink is transferred onto the ink application roller that is in contact with the plate cylinder.
Conventionally, some types have been publicly known as unit for breaking emulsion. One of the types (Japanese Unexamined Patent Application Publication No. 53-36308) is such that emulsion of emulsion ink is broken by actions of cooling unit and shearing force applying unit, which are provided at an ink application roller in an ink-furnishing apparatus, and another one thereof (Japanese Unexamined Patent Application No. 55-7453) is such that emulsion is broken by cooling and with an intensive shearing force brought about by an ink application roller in an ink-furnishing apparatus and an adjusting roller whose surface is hydrophilic.
Where an offset press is used, in which ink is continuously fed and emulsion ink is used, since the ink furnishing roller continuously rotates and the rotation speed thereof is comparatively fast, a rod-like ink clump (see FIG. 21, this is referred to as an xe2x80x9cink rollxe2x80x9d) may be formed in parallel to the axial direction of the ink furnishing roller in an ink reservoir. If an ink roll is generated, fluidity and agitation of ink in the ink reservoir is hindered, ink existing in a comparatively surface layer of the ink roll is only consumed without being replaced by ink inside the ink roll. Therefore, in the case of a two-constituent blended liquid of ink and an aqueous constituent such as emulsion ink, balance between the ink and the aqueous constituent of emulsion ink, which is measured and fed to the ink application roller, is varied to adversely influence the printing performance (in particular, smirching resistance).
In order to break down the above-described emulsion, it is necessary that emulsion ink is cooled down and a shearing force is applied thereto. However, ink becomes remarkably hard due to a lowering in ink temperature (generally called xe2x80x9cink condensingxe2x80x9d), wherein it becomes difficult to transfer ink, thereby causing such a problem of printing drawbacks such as shortage in density, whiteout, etc. Therefore, it is not desired that cooling is preferentially used as unit for breaking down emulsion,
Also, for application of a shearing force, ink has been subjected to slipping between rollers. However, since stability of emulsion is increased due to an increase in ink temperature resulting from friction by slipping between rollers, it becomes difficult for the emulsion to be broken down. Therefore, the relationship between a slipping amount and an effect to break down emulsion is not proportionate, wherein the effect of breaking down emulsion is limited even if the slipping amount is increased, and a sufficient effect of emulsion breakage cannot be obtained. Furthermore, the cohesion power of ink is lowered in line with an increase in ink temperature, wherein such a problem arises in that printing drawbacks such as ink fill-in and scumming, etc., occur.
Although an increase in ink temperature due to slipping between the above-described rollers can be suppressed by concurrently employing the above-described cooling unit, it becomes necessary to prepare cooling unit whose cooling output is large since the heat generation amount due to slipping is large.
In addition, the method for slipping between rollers results in remarkable wearing of the rollers. Further, such a problem arises in that, if an offset press is operated with no ink provided by mistake, the roller will be instantaneously damaged.
The present invention was developed in view of the above-described situations. It is therefore a first object of the present invention to provide an ink-furnishing apparatus that is able to suppress or prevent ink rolls from occurring in an ink reservoir, secure satisfactory fluidity and agitation of ink in the ink reservoir, and carry out smooth measuring of ink and furnishing thereof to an ink furnishing roller, and an offset printing method using the same.
The present invention was developed in view of the above-described and other problems, and it is therefore a second object of the present invention to provide an ink-furnishing apparatus and an offset printing method, which are able to apply an effective shearing force in order to break down emulsion, can be easily controlled during operations, where an increase in ink temperature and wearing of rollers are only slight, and there is little possibility for the rollers to be damaged.
In order to solve the objects, according to a first aspect of the present invention, there is provided an ink furnishing apparatus comprising: an ink fountain storing ink; an ink furnishing roller engaged with the ink fountain, withdrawing the ink in the ink fountain by rotations thereof and furnishing the ink to a printing plate; and an ink contacting member formed at substantially an entire length of the ink fountain in a width direction thereof and contactable with the ink in the ink fountain.
According to a second aspect of the present invention, there is provided an ink furnishing apparatus as set forth in the first aspect of the present invention, wherein the ink contacting member is disposed to be spaced from the ink furnishing roller.
According to a third aspect of the present invention, there is provided an ink furnishing apparatus as set forth in the first or second aspect of the present invention, wherein the ink contacting member is disposed substantially in parallel to an axial line of the ink furnishing roller.
According to a fourth aspect of the present invention, there is provided an ink furnishing apparatus as set forth in any one of the first to third aspects of the present invention, wherein the ink contacting member is divided into a plurality of sections along the width direction of the ink fountain, or includes a plurality of molded members juxtaposed along the width direction of the ink fountain.
According to a fifth aspect of the present invention, there is provided an ink furnishing apparatus as set forth in any one of the first to fourth aspects of the present invention, wherein the portion of the ink contacting member, wherein a portion of the ink contacting member contacting with the ink inclined with respect to an axial line of the ink furnishing roller.
According to a sixth aspect of the present invention, there is provided an ink furnishing apparatus as set forth in any one of the first to fifth aspects of the present invention, wherein the ink contacting member includes a baffle plate or roller.
According to a seventh aspect of the present invention, there is provided an ink furnishing apparatus as set forth in any one of the first to sixth aspects of the present invention, wherein a surface of the ink contacting member defines grooves thereon, or a surface of the ink contacting member defines inclined grooves thereon with respect to the axial line of the ink furnishing roller.
According to an eighth aspect of the present invention, there is provided an ink furnishing apparatus as set forth in any one of the first to seventh aspects of the present invention, wherein the ink contacting member includes a drive unit for moving or rotating the ink contacting member.
In addition, according to the above construction, it is preferable that there is provided a printing machine with the above ink furnishing apparatus.
According to the above-described construction, since ink contacting member is provided, it is possible to suppress or prevent ink rolls from being formed in the ink fountain, wherein ink fluidity and agitation ability of ink in the ink fountain can be secured, and favorable ink metering and furnishing to an ink forming roller are enabled.
In order to solve the objects, according to a ninth aspect of the present invention, there is provided an ink-furnishing apparatus comprising: an ink fountain storing emulsion ink therein; an ink forming roller contacting with a printing plate and furnishing the emulsion ink to the printing plate; a shear controlling roller contacting with the ink furnishing roller and bringing about emulsion breakage by applying shear to the emulsion ink; and a nip pressure controlling unit controllable a nip pressure at a contact point between the shear controlling roller and the ink forming roller during operation.
According to a tenth aspect of the present invention, there is provided an ink-furnishing apparatus as set forth in the ninth aspect of the present invention, further comprising: an ink furnishing roller furnishing the emulsion ink to the ink forming roller; and an ink furnishing unit withdrawing the emulsion ink with a predetermined membrane thickness from the ink fountain in cooperation with the ink furnishing roller and forming the emulsion ink on the surface of the ink furnishing roller.
According to an eleventh aspect of the present invention, there is provided an ink-furnishing apparatus as set forth in the ninth aspect of the present invention, further comprising an ink furnishing unit withdrawing the emulsion ink with a predetermined membrane thickness from the ink fountain in cooperation with the ink forming roller and forming the emulsion ink on the surface of the ink forming roller.
According to a twelfth aspect of the present invention, there is provided an ink-furnishing apparatus as set forth in any one of the ninth to eleventh aspects of the present invention, wherein unit for agitating the emulsion ink is fed in the ink fountain.
According to the present invention, there is provided a printing method comprising steps of: furnishing emulsion ink stored in an ink fountain to an ink forming roller contacting with a printing plate of an offset press; contacting a shear controlling roller onto the emulsion ink on the ink forming roller; controlling a nip pressure at a contact point between the ink forming roller and the shear controlling roller; applying a shear to the emulsion ink by the shear controlling roller, the shear bringing about emulsion breakage at the contact point; and furnishing emulsion ink on the ink forming roller to the printing plate while maintaining appointed emulsion breakage of the emulsion ink. Also, it is preferable that, while adding an agitation effect in the axial direction of the ink furnishing roller for furnishing emulsion ink to the above-described ink furnishing roller with respect to ink stored in the above-described ink fountain, ink is fed to the above-described ink furnishing roller.
According to the ink-furnishing apparatus according to the ninth to twelfth aspects and offset printing method according to the thirteenth aspect, since the nip pressure controlling unit that is able to control the nip pressure of the shear controlling roller to break down emulsion during operations is provided, it is possible to apply an effective shearing force to break down emulsion by re-adjusting the nip pressure without stopping the operations even in a case where the shear fluctuates during the operation and the printing quality is adversely influenced.
Since the apparatus according to the twelfth aspect is provided with ink agitating unit in the ink fountain, ink rolls (rod-like ink clump parallel to the axial direction of the ink furnishing roller) formed in the ink fountain can be prevented from being generated. Therefore, it is possible to secure fluidity and agitation of ink in the ink fountain, wherein it becomes possible to satisfactorily measure and furnish ink to the ink furnishing roller. In an offset press employing emulsion ink, generally, ink rolls are likely to occur in the ink fountain due to continuous furnishing of ink and high-speed rotations of the ink furnishing roller. According to information of the present inventor, it is confirmed that ink rolls are generated at a roller speed of several hundred millimeters per second or more. Ink existing in a comparatively surface layer of ink rolls is consumed without being replaced with ink inside the ink rolls, wherein, with a two-constituent mixture liquid such as emulsion ink, balance of ink to an aqueous constituent, which are measured and fed to the ink furnishing roller is changed due to generation of ink rolls, and a lowering in the printing quality is remarkable in comparison with a case where normal ink is used. Therefore, since fluidity and agitation of ink in an ink fountain are secured by providing ink agitating unit, the constituent balance of the emulsion ink is not broken up, wherein satisfactory furnishing of ink to the ink furnishing roller can be brought about.